This invention relates to a bilayer non-woven porous substrate in which the dominant layer is composed of organic fibers and a thinner layer thereon composed of a cured silicone resin. While acrylated silicone resin is greatly preferred, other silicone resins having release properties can be employed in the present invention in place of acrylated silicone resins. When a pressure sensitive adhesive is applied to the organic fiber surface, a pressure sensitive tape results that can be wound upon itself. In the prior art, pressure sensitive tapes of this type have required liners to be placed between the pressure sensitive surface and the front face of the tape notwithstanding the availability of a variety of low adhesion backsizes.
Silicone resins have been conventionally applied as an organic solution or water based dispersion. However, porous non-woven materials when treated in this manner do not produce a substrate of the type provided by this invention. Instead, the fibers of the organic polymer are covered at least partially with the silicone resin throughout which is undesirable, i.e., the coating soaks into the porous backing material. The present invention overcomes this problem.
Coatings often drastically reduce the porosity of fibrous substrates. Maintaining porosity at a high level is very important especially in the case of medical adhesive tapes, e.g., to prevent moisture from being trapped beneath the tape. The porous nature of the bilayer provided by the present invention is substantially the equivalent to the porosity of a fibrous organic polymer matrix prior to the application of a coating thereon.